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The aim of my experiment is to investigate how the mass of potato (concentration of catalase) affects the rate of reaction with hydrogen peroxide.

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AN INVESTIGATION INTO HOW THE MASS OF POTATO AFFECTS THE RATE OF REACTION OF THE ENZYME CATALASE SKILL AREA P: PLANNING Aim: The aim of my experiment is to investigate how the mass of potato (concentration of catalase) affects the rate of reaction with hydrogen peroxide. Introduction: In a chemistry lesson I learnt that an enzyme is a biological protein that acts as a catalyst in living cells. A catalyst is a substance that changes the rate of reaction without being used up. Therefore it can be re-used. Catalysts help substances to react more easily by breaking and forming bonds between atoms. Most catalysts speed up their reactions. This is because particles need less energy to react, so the reactions proceed more quickly. The reaction I am investigating occurs in humans because hydrogen peroxide is a by-product of some chemical reactions that take place in our cells. The reason that hydrogen peroxide needs to be broken down is because it is very poisonous as H2O2 but is harmless as water and oxygen. Here is an equation to show this reaction: Hydrogen Peroxide Oxygen + Water 2H2O2 O2 + 2H2O However in my investigation I will be using potatoes as it contains living cells and the enzyme catalase. Key Variables: In the experiment I could have varied the following factors to find out how the rate of reaction is affected. *Concentration of hydrogen peroxide: When the concentration of hydrogen peroxide is increased, there are more particles per unit volume. Therefore, the frequency of collisions increases, and the rate of the reaction increases. To keep the concentration constant I will use the same concentration throughout the experiment. *Volume of hydrogen peroxide: If the volume of hydrogen peroxide is large then that means that there is more reacting particles than in a smaller volume of hydrogen peroxide. Therefore more collisions per second will occur making the reaction fast. To keep the volume of hydrogen peroxide constant I will use 20ml of hydrogen peroxide in every experiment. ...read more.


I will also be able to obtain an average from these results. Plan Apparatus: *Potatoes *Hydrogen Peroxide *100ml Measuring cylinder *Conical flask *Beaker *Beehive shelf *Bung (with a small glass tube and delivery tube attached to it.) *Thermometer (100�C) *Water *Mincing machine *1 small water bath *1 large water trough Diagram: Method: The apparatus will be set up as shown in the diagram. A few potatoes will be minced using a mincing machine for about 30seconds. 127ml of water will be measured using a measuring cylinder and transferred into a small water trough. Then a large water trough will be filled just above halfway and a beehive shelf will be placed in the middle of the large trough. A measuring cylinder then will be filled with water and placed upside down over the beehive shelf making sure that there are no air bubbles in the measuring cylinder. The conical flask will be placed on the balance and the scale will be reset to zero. Minced potato will be added to the conical flask until the scale reads 2.5g. The bung with the small glass tube and delivery tube attached will be tightly secured into the conical flask assuring that no gas will escape. The conical flask will then be placed into the small water trough. The temperature of the water in the small trough will be measured and the temperature will be kept constant throughout the experiment. If the water turns cold then cold water will be added and vice versa. 20ml of hydrogen peroxide will be measured using a syringe and will be slotted into the small glass tube in the bung. The stopwatch will be started immediately when the hydrogen peroxide is injected into the conical flask. After 30 seconds the amount of gas collected in the measuring cylinder will be entered into my results table. I will make sure that I read the measuring cylinder at eye level and at the bottom of the meniscus. ...read more.


I have no anomalous results as all the points are close to the line I have drawn on the graph not all of the points are on the line showing experimental errors. Many variations of this experiment could back up the evidence I already have. The independent variables could be changed. For instance; the water temperature could be varied, the hydrogen peroxide concentration could be altered or the surface area could be varied more by using differently shaped potato samples. Further testing, using more catalase or allowing the reaction to continue for longer would show if the reaction would level off. Obviously, I could improve upon the same experiment that I have already done by repeating it five times and therefore getting a better average. I could have taken more readings so that my graph had more points and the trend could be seen more clearly. I think that my method for finding how the concentration of catalase affects the rate of the reaction between catalase and hydrogen peroxide was the best possible one under school laboratory conditions. I could improve my experiment by using a gas syringe instead of an upside down measuring cylinder filled with water. As the gas syringe is specially made for collecting gas, this apparatus will be more reliable for collecting oxygen for the investigation. If I were working with a partner, this would also make a difference in the results as one person could be observing the experiment whilst the other was looking at the time. Not only would the results be more reliable, but also the investigation would be carried out faster allowing more time for more readings to be taken down. In between the person who was mincing the potato was changed in my investigation and so the potato could be minced differently at times. Although this did not make a huge difference to my results, I think that if the same person does it throughout the experiment then the results plotted on the graph me be mre closer to the line or even on the line. ...read more.

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